The Effect of the Color of Granite on its Natural Radioactivity

Living environment and applied building materials in dwellings contain various amounts of radioactive elements. Knowing about the distribution and the level of radiation in the environment is very important to evaluate the effects of radiation on the human. In this study, the level of radioactive nuclei in the granite was assessed according to the color of the stone. 13 different types of granite used in city of Isfahan (Iran) dwellings were selected, turned to powder, packaged in Marinli dishes and sealed accordingly. The International Atomic Energy Commission instructions were applied for sampling and all other steps of the survey. The dishes were kept for 5 weeks before spectroscopy, to obtain equivalent amount of uranium and thorium nuclides. Then, the gamma-spectroscopy of each sample was collected by HPGe (high purity germanium detector) for 12 hours and categorized based on its energy level. Finally, the special activity of the radiating nuclides in each sample was obtained. Measuring natural radioactivity, including nucleus radioactivity of 238U, 232Th, 40K based on Bq/kg unit, was done. The specific average radioactivity concentration of each radiating nuclei was evaluated, too. The reported special activities for 238U were less than malondialdehydc (MDA) level for green, 65.72 Bq/Kg for white, 57.26 Bq/kg for red, and 24.31 Bq/kg for black granites. The measured special activities for 232Th were 113.36, 84.31, and 34.28 Bq/kg, and less than MDA level for white, red, black and green granites, respectively. Besides, the measured special activities for 40K were 53.16, 525.82, 897.37, and 1243.28 Bq/kg for green, black, red, and white granites, respectively. White granite sample has the highest special activity for the three nuclides, 238U, 232Th, and 40K. Also, the lowest special activity for these nuclides was found in green stones and the red granite had an intermediate activity.